1. Field of the Invention
The present invention relates in general to a device for turning an object through 90 degrees, and more particularly to such a 90.degree. turning device adapted to turn an object material or article while it is transferred by a conveyor or other type of transfer equipment.
2. Discussion of the Prior Art
An example of a device used for turning an article in the process of being transferred is disclosed in Publication No. 57-61051 (published Dec. 27, 1982) of examined Japanese Utility Model Application, wherein a rotary plate is rotatably mounted on a moving member which is movable along a linear path. The rotary plate is provided with a plurality of cam follower rollers, which are adapted to sequentially engage recesses or cutouts formed in a fixed cam plate, so that the rotary plate is rotated while it is moved along the linear path. Another known turning device uses a rack-and-pinion arrangement. These known turning devices are comparatively complicated in construction and suffer from a relatively high cost of manufacture.
In view of the conventional turning devices described above, the assignee of the present application developed a 90.degree. turning device 100 as shown in FIG. 11. This turning device 100 uses simple cams having straight surfaces, and a cam follower engageable with the cam surface. Described more specifically, the 90.degree. turning device 100 uses an elongate turning member 102 which is supported rotatably about the axis of a shaft 114. The turning member 102 has a cam follower 104 at one of its opposite ends. The cam follower 104 is engageable with a first cam surface 108 of a first cam 106, and a second cam surface 112 of a second cam 110, while the turning member 102 is moved along a linear path. With the cam follower 104 engaging the first and second cam surfaces 108, 112, the turning member 102 is turned about the shaft 114.
When an article being transferred is turned to change its posture by a turning device, it is desirable that the article is turned at a constant angular velocity. A change in the angular velocity of the turning device means a certain degree of acceleration, which may cause the article to slide or otherwise move out of position on the turning device or even fall from the turning device. A curve indicated in FIG. 9 is a path or locus described by a point P on a circle when a straight line OP between a center O of the circle and the point P on the circumference of the circle is rotated about the center O, while the center O is moved along a straight path OA. The curved path is an ideal path that is to be taken by the cam follower 104 to cause the turning member 102 to be rotated at a constant angular velocity, where the centerline or axis of rotation of the shaft 114 of the turning member 102 lies on the center O of the circle while the center of the cam follower 104 lies on the point P. The ideal curved path to be taken by the cam follower 104 is also indicated in FIG. 10 in two-dot chain line. The turning member 102 can be rotated at a substantially constant angular velocity, if the angles of inclination of the first and second cam surfaces 108, 112 are determined so as to approximate to that of the ideal curved path. The cam surfaces 108, 112 of the turning device 100 of FIG. 11 are adapted to substantially follow intermediate portions of the ideal curved path.
Since the cam surfaces 108, 112 are straight, it is impossible to guide the cam follower 104 smoothly along a central portion of the ideal curved path at which the path is turned or bent. The straight cam surfaces 108, 112 cannot faithfully follow the turned central portion of the curved path. In other words, the cam follower 104 cannot be adequately guided after the cam follower 104 leaves the first cam surface 108 and before it comes into contact with the second cam surface 112. Accordingly, the turning velocity of the turning member 102 is suddenly increased upon abutting contact of the cam follower 104 on the second cam surface 112, whereby the turning member 102 undergoes a high degree of acceleration, which may cause the above-indicated inconvenience in turning the object article mounted on the turning device.